Bleaching of cotton



Patented May 28, 1940 BLEACHING OF COTTON Thomas E. Bell, Philadelphia, Pa., assignor to E, I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application December 1, 1938, Serial No. 243,408

1 Claim. (01. 8111) ton with bleaching baths containing active oxygen yielding substances as bleaching agents consists in subjecting the cotton goods to the action of the bleaching bath in an iron kier lined with cement or silica. The bleaching bath is usually prepared and stored outside of the kier in a separate storage tank and fed to the kier after the kier has been loaded with the cotton goods. The cotton goods may be if desired pretreated, for example with caustic, before they are subjected to the bleaching process proper. The bleaching is usually carried out by circulating the bleaching liquid by means of a suitable pump through the kier for about 5 to 8 hours at temperatures of about 180 F. After completion of the bleaching process the liquid is drained off and led to the sewer while the goods are washed in the kier and then are unloaded from the kier preferably through a suitable washer. To decrease the cost of the bleaching process the bleaching baths were generally prepared with minimum amounts of the bleaching agent so as to obtain a waste liquid which is as free as possible from undecomposed bleaching agent.

An object of the invention is to provide an improved process for bleaching cotton with bleaching baths containing active oxygen yielding substances as bleaching agents whereby the waste of bleaching agents is substantially decreased. Further objects will be apparent hereinafter.

The objects of my invention are accomplished by adding to a bleaching bath which has been used in a prior bleaching treatment of cotton sufficient amounts of bleaching agents and other additional agents to activate the bath for subsequent treatment of unbleached cotton goods. As stated above, heretofore bleaching baths which have been used in a bleaching treatment for cotton have been disposd of after a single bleaching treatment and the only attempt to decrease the bleaching costs consisted in keeping the addition of bleaching agents to the bath as low as possible. 5

Replenishing of cotton bleaching baths heretofore has been held to be impractical. Cotton bleaching baths after a single use as a fact gener ally do not contain large amounts of bleaching agents and have a dirty appearance. Since by 10 using minimum additions of bleaching agents to the fresh bath it can be obtained that the used baths contain less than 15% of the initial amount of the bleaching agent it has been believed that further treatment of the exhausted bleaching bath would have too little economical advan- 15 tages to justify the risk of using these con taminated exhausted baths.

My invention is based on the discovery that replenishing of cotton bleaching baths containing active oxygen yielding compounds as bleach- 20 ing agents not only considerably improves the economy of the bleaching process where considerable amounts of bleaching agents are left in the used bleaching bath, but also effects substantial economies where exceedingly small amounts such as, e. g., 10% or even less, are left in the bath. This seems to be due to the fact that such exhausted bleaching baths offer an especially advantageous medium for bleaching of cotton. Moreover, the use of such an exhausted bleaching bath for further treatment of cotton goods by replenishing the exhausted bath has the advantage that the concentration of the bleaching bath in bleaching agents can be regulated according to the desired activity of the bleaching bath to any desired high concentration without affecting the economy of the process since residual active oxygen contained in the used baths will be utilized in a subsequent bleaching process. Thus, for example, when bleaching colored yarn fabrics, where a minimum of hydrogen peroxide is used for economic reasons, danger of reduction of color occurs if the hydrogen peroxide is exhausted. This danger is completely avoided by the process of my invention which allows the use of any concentration of the bleaching bath.

It is also known that better finishing results if the ratio of bleaching liquor to treated goods is not too small. I-Ieretofore, in the interest of economy, this ratio has been kept as low as possible. The process of my invention, however, also allows for adjusting this ratio to an optimum degree, since the residual bleaching agent will be conomically utilized in a subsequent bleaching treatment. It has also been found that the contaminations contained in the bleaching bath have no appreciable deterimental efiect on the goods to be treated and that the bleaching baths can be replenished repeatedly, e. g., five times and more and still provide excellent bleaching. Replenishing of the bleaching bath not only ofiers material saving in bleaching agents but also in addition agents. Furthermore, such practice increases the heat economy of the process and decreases the difiiculties encountered with the disposal of large amounts of Waste liquids.

My invention is further illustrated by the following examples:

Emample I Conventional kiers were used for the following series of experiments, the ratio of cotton goods to bleaching liquid used being about 40 gallons bleaching liquid to 100 lbs. cotton goods. The goods were first wet out in the usual manner and piled in the kier. The goods were subjected to the action of the bleaching bath for about 5 to 8 hours at about 180 F. After sufficient bleaching was obtained the bleaching bath was drained ofi and returned to a stainless steel storage vessel and then the bleached cotton goods were washed and unloaded in the usual manner. The exhausted bleaching bath was replenished in the storage vessel and fed to another kier which has been loaded with a new charge of unbleached cotton goods. In the following table the results of cotton bleaching tests are given. In the table under each run number the amounts of goods treated and the amounts of chemicals added to the bleaching bath are given. The amounts of bath constituents given under run No. l are those contained in the original bleaching bath while under run No. 2 and run No. 3 the replenishing amounts for the various bath constituents are given.

Table moon-ga s (HUI As can be seen from this table, by replenishing the bath considerable savings in chemicals are obtained. The whiteness of the bleached cotton goods was highly satisfactory in each run. Also considerable amounts of steam and water were saved. The average water temperature is about 50 F. and in the conventional bleaching process the bleaching bath therefore has to be raised in the kier to 180 F., i. e., an increase of 130 F. When carrying out the process described in this example the replenished liquor when used immediately following separation of the cotton goods and replenishment is at a temperature of about 120 F., necessitating a raise of only 60 F.

Example II A series of five bleaching runs was made under the same conditions as in Example I, the constituents of the bleach bath being replenished as required between each run. The results of this series are shown in the following table, the bleaching bath under run No. 1 again being the original bleaching bath.

The bleaching results with all runs were equally satisfactory.

The reduction of Waste liquids was 80%.

Various control tests have shown that in general the average recharge will consist of 60% of the original alkali, including the sodium peroxide, and 70 to 75% of the original hydrogen peroxide, and 50% of the original kier assistants.

My invention is not restricted to the expedients and the chemicals used in the above examples. In its broad aspect it is applicable wherever cotton goods are bleached with bleaching baths containing active oxygen yielding substances as bleaching agents. As bleaching agents, for example, hydrogen peroxide, metal peroxides, per salts, organic per compounds or any other desired active oxygen yielding substances may be used alone or in combination. I prefer, however, to use bleaching baths containing hydrogen peroxide or alkali metal peroxides or hydrogen peroxide and alkali metal hydroxides as bleaching agents. Addition agents of any desired property may be added to the bleaching bath such as for example alkaline substances, stabilizers, softening agents, soaps, detergents or kier assistants. Instead of working in a kier the cotton goods may also be treated in open vats or in any other desired apparatus. The bleaching baths also need not be replenished to their original composition but may also be replenished to any other desired composition if so desired. It has been found that the bleaching baths even after six replenishments usually still give highly satisfactory results. Various modifications of the process of my invention will be apparent to those skilled in the art.

I claim:

In the process of bleaching cotton in a kier with a bleach bath containing hydrogen peroxide, sodium silicate being also present in said bleach bath as an alkalining and buffering agent, the steps which comprise: bleaching said cotton goods positioned within a kier with said bleach liquor at an elevated temperature in the neighborhood of 180 F. for a period of five to eight hours, there being present approximately 40 gallons of bleach liquor per one hundred pounds of cotton goods; removing said cotton goods from said bleach bath at the completion of said bleaching, said used bleach bath having a hydrogen peroxide concentration not in excess of 10% of its original concentration; adding to said used bleach bath further amounts of hydrogen peroxide for wwuw \wu new-w n our PU CL C the purpose of replenishing the peroxide concenhood of 180 F. for a period of from five to eight tration of said bath to a value equivalent to subhours, there being present approximately 40 galstantially its original concentration; adding to lons of bleach liquor per one hundred pounds of said replenished bath additional quantities of soeotton goods being treated; and repeating said 5 dium silicate as alkalining and bufiering agent; process whereby said bath is replenished and re- 5 treating further amounts of unbleached cotton utilized at least four additional times. goods positioned in a kier with said replenished bleach bath at a temperature in the neighbor- THOMAS E. BELL. 

